INVESTMENTS - Debt Securities Held-to-Maturity (Details) - USD ($)	1 Months Ended
	Aug. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt Securities Held-to-maturity
Amortized cost, net		$ 96,065,000,000		$ 80,775,000,000
Gross unrealized gains		3,200,000,000		1,557,000,000
Gross unrealized losses		251,000,000		109,000,000
Fair value		99,014,000,000		82,223,000,000
Allowance for credit losses on HTM debt securities		98,000,000	$ 107,000,000	0
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Debt Securities Held-to-maturity
Amortized cost, net		46,833,000,000		46,637,000,000
Gross unrealized gains		2,422,000,000		1,047,000,000
Gross unrealized losses		12,000,000		21,000,000
Fair value		49,243,000,000		47,663,000,000
Mortgage-backed securities - Non-U.S. residential
Debt Securities Held-to-maturity
Amortized cost, net		1,099,000,000		1,039,000,000
Gross unrealized gains		3,000,000		5,000,000
Gross unrealized losses		2,000,000		0
Fair value		1,100,000,000		1,044,000,000
Commercial
Debt Securities Held-to-maturity
Amortized cost, net		774,000,000		582,000,000
Gross unrealized gains		1,000,000		1,000,000
Gross unrealized losses		1,000,000		0
Fair value		774,000,000		583,000,000
Mortgage-backed securities
Debt Securities Held-to-maturity
Amortized cost, net		48,706,000,000		48,258,000,000
Gross unrealized gains		2,426,000,000		1,053,000,000
Gross unrealized losses		15,000,000		21,000,000
Fair value		51,117,000,000		49,290,000,000
U.S. treasury securities
Debt Securities Held-to-maturity
Amortized cost, net		14,917,000,000
Gross unrealized gains		2,000,000
Gross unrealized losses		26,000,000
Fair value		14,893,000,000
Fair value of securities transferred from AFS to HTM	$ 13,100,000,000
Securities transferred from AFS to HTM, unrealized gain position	$ 144,000,000
State and municipal
Debt Securities Held-to-maturity
Amortized cost, net		9,197,000,000		9,104,000,000
Gross unrealized gains		693,000,000		455,000,000
Gross unrealized losses		17,000,000		28,000,000
Fair value		9,873,000,000		9,531,000,000
Foreign government
Debt Securities Held-to-maturity
Amortized cost, net		1,739,000,000		1,934,000,000
Gross unrealized gains		74,000,000		37,000,000
Gross unrealized losses		0		1,000,000
Fair value		1,813,000,000		1,970,000,000
Asset-backed securities
Debt Securities Held-to-maturity
Amortized cost, net		21,506,000,000		21,479,000,000
Gross unrealized gains		5,000,000		12,000,000
Gross unrealized losses		193,000,000		59,000,000
Fair value		$ 21,318,000,000		$ 21,432,000,000